Organometallics 1986, 5, 1778-1785
1778
Metal Complexes of Sulfur-Containing Ligands. Synthesis and Properties of a Series of Rhenium-Substituted Sulfonium Salts Fred B. McCormick,*1a7b William B. Gleason,la Xiande Zhao,'' Poh Choo Heah,lc and J. A. Gladysz*'bsc 3M Corporate Research Laboratories, St. Paul, Minnesota 55 144, Department of Chemistry, University of California, Los Angeles, California 90024, and Department of Chemistry, University of Utah, Salt Lake City, Utah 84112 Received January 13, 1986
Reaction of [ (a5-C5H5)Re(NO)(PPh3)(=CH,)]+PF6(1, -78 "C) with CH3SCH3gives sulfonium salt [ (q5-C5H5)Re( NO) (PPh3)(CH2S(CH3),)]+PF6-(2, 90-95 % ). Variable-temperature NMR data show that CH,SCH, reversibly gives from 2 with AG*262 = 14.2 kcal/mol and AC*zss= 12.9 kcal/mol. Reaction of 2 with PPh, and pyridine give [ (q5-C5H5)Re(NO)(PPh3)(CH2PPh3)]+PF6(4, 76%) and [(q5-C5H5)Re-
-
(NO)(PPh3)(CH,N(CH),CH)]+PF6( 5 ) , respectively. Reaction of 2 with RS- gives (q5-C5H5)Re(NO)(PPh,)(CH,SR) (6,79-95%; R = CH, (a), C6H5(b),CH2C6H5(c)).Reaction of 1 or 2 with 6a gives binuclear sulfonium salt [ (q5-C5H5)Re(NO)(PPh3)(CH2-)j2S+CH3 PF6- (7+PF6-,89-92%) as a 2:l:l mixture of diastereomers. Treatment of 7+PF6-with NaI/CH3CN gives 7+I-, which crystallizes as one diastereomer as shown by X-ra crystallography. Crystal data: orthorhombic, Pnma; a = 18.348 (6) A, b = 20.767 (2) A, c = 13.944 (2) $I; 2 = 4. Reaction of 7+PF6-with PPh, gives 4 (90%)and 6a (71%). Pyrolysis of 7+PF6(80 OC, 8 h) gives ($-C,H,)Re(NO)(PPh,)(CH,) (8, 84%) and [(q5-C5H5)Re(NO)(PPh3)(=CHSCH3)]+PF; (9,82%1. Reaction of 1 with Na2S gives trinuclear sulfonium salt [ (I~~-C~H~)R~(NO)(PP~,)(CH,-)],SPF~ (10, 84%). Complex 10 reacts only sluggishly with PPh, (65 OC). These reactions show that the (7 C,H5)Re(NO)(PPh3)moiety significantly enhances the basicity of sulfide sulfur atoms that are p to it.
Introduction The preparation and study of metal complexes of sulfur-containing ligands is of fundamental interest and can aiso be expected to further understanding of the sulfur poisoning of metal catalyst^,^-^ metal-catalyzed hydrodesulf~rization,~-~ and coal liquefication/gasification chemistry. We have synthesized and extensively examined the physical and chemical properties of rhenium alkylidene complexes of the formula [ (q5-C5H5)Re(NO)(PPh3)(= CHR)]+.8 Since coordinated alkylidenes are ubiquitous intermediates in metal-catalyzed reaction^,^ we have undertaken a study of several types of sulfurlo and other chalcogen'l derivatives. In this paper, we describe reactions of the methylidene complex [ (T~-C,H,)R~(NO)(1) (a) 3M; correspond with F.B.M. at this address. (b) UCLA. (e) University of Utah; correspond with J.A.G. at this address. (2) (a) Bartholomew, C. H.; Agrawal, P. K.; Katzer, J. R. Adu. Catal. 1982, 31, 135. (b) Anderson, R. B. The Fischer-Tropsch Synthesis; Academic Press: Orlando, 1984; Chapter 6. (3) (a) Lesch, D. A.; Richardson, J. W.; Jacobson, R. A.; Angelici, R. J. J. Am. Chem. SOC.1984, 106, 2901. (b) Spies, G. H.; Angelici, R. J. J . Am. Chem. SOC.1985, 107, 5569. (4) (a) Bucknor, S. M.; Draganjac, M.; Rauchfuss, T. B.; Ruffing, C. 1984,106,5379. (b) J.; Fultz, W. C.; Rheingold, A. L. J. Am. Chem. SOC. Draganjac, M.; Ruffing, C. J.;Rauchfuss, T. B. Organometallics 1985,4, 1909. (5) Legzdins, P.; Slnchez, L. J . Am. Chem. SOC.1985, 107, 5525. (6) Rakowski DuBois, M. J. Am. Chem. SOC.1983,105, 3710. (7) Kubas, G. J.; Ryan, R. R. J. Am. Chem. SOC.1985, 107, 6138. (8) (a) Tam, W.; Lin, G.-Y.; Wong, W.-K.; Kiel, W. A.; Wong, V. K.; Gladysz, J. A. J . Am. Chem. SOC.1982, 104, 141. (b) Kiel, W. A.; Lin, G.-Y.; Constable, A. G.; McCormick, F. B.; Strouse, C. E.; Eisenstein, 0.; Gladysz, 3. A. Ibid. 1982,104,4865. (c) Kiel, W. A.; Lin, G.-Y.; Bodner, G. S.; Gladysz, J. A. Ibid. 1983,105,4958. (d) Patton, A. T.; Strouse, C. E.; Knobler, C. B.; Gladysz, J. A. Ibid. 1983, 105, 5804. (e) Merrifield, J. H.; Lin, G.-Y.; Kiel, W. A.; Gladysz, J. A. Ibid. 1983,105,5811. (0Kiel, W. A.; Buhro, W. E.; Gladysz, J. A. Organometallics 1984, 3, 879. (9) See, inter alia: (a) Herrmann, W. A. Angew. Chem., Int. Ed. Engl. 1982,21, 117. (b) Ivin, K. J. Olefin Metathesis; Academic Press: New York, 1983. (10) (a) McCormick, F. B.; Gladysz, J. A. J. Organomet. Chem. 1981, 218, C57. (b) Buhro, W. E.; Patton, A. T.; Strouse, C. E.; Gladysz, J. A.; McCormick, F. B.; Etter, M. C. J . Am. Chem. SOC.1983, 105. 1056. (11) McCormick, F. B. Organometallics 1984, 3, 1924.
0276-7333/86/2305-1778$01.50/0
(PPh3)(=CH2)]+PF6-(1) with several classes of sulfur nucleophiles. A series of three novel sulfonium salts, [(17'-C5H5)Re(NO)(PPh3)(CH,-)],S+(CH3),_, (n = 1-3), have been synthesized and their properties and reactivities studied and contrasted. An X-ray crystal structure of the salt with n = 2 is described. A portion of this work has been communicated.loa
Results I. Mononuclear Sulfonium Salts. Reaction of (($-C5H5)Re(NO)(PPh3)(=CHZ)]+PF6(1, generated in situ in CH2C1JBawith CH3SCH3at -78 OC gave the sulfonium salt [ (q5-C5H5)Re(N0)(PPh3)(CH2S(CH3),)]+PF, (2) in 90-95% yields after workup and recrystallization (eq 1). The structure of this compound followed readily from
1
2
its spectroscopic properties (Experimental Section). These included two SCH, resonances in low-temperature lH and I3C NMR spectra, an upfield ReCH2S 13CNMR resonance (4.1 ppm), and v5-C5H5IH (6 5.25) and 13C (90.8 ppm) NMR resonances. These chemical shifts, and the IR v ~ - ~ at 1657 cm-' (CH2Clz,s), were similar to those found for phosphonium salts derived from the addition of phosphines to 1.8a Reaction of 1 with C6H5CH2SCH3gave the less stable sulfonium salt [ (q5-C5H5)Re(NO) (PPh3)(CH2S(CH3)(CH2C6H5)]+PF& (3), which was isolable in crude form but decomposed upon attempted purification. Complex 3 exhibited 'H NMR properties very similar to 2 (6, CD,CN, 60 MHz): 7.50-7.15 (m, 4C6H5), 5.30 (s, C5H5),4.02 (s, C&$ff2), 3.58 (v br s, ReCH,S), 2.28 (s, CH,). The re0 1986 American Chemical Society
Metal Complexes of Sulfur-Containing Ligands action of 1 with dibenzyl sulfide did not yield a stable sulfonium salt. No evidence for sulfonium salt formation was observed when alkylidene complexes ac- [ (q5-C5H5)Re(NO)(PPh,)(=CHR)]+PFc (R = C6H5,CH3)8b9cwere treated with CH3SCH3 a t room temperature. The reversibility of eq 1 was probed by variable-temperature 'H and 13C NMR spectroscopy in CD2C12. The -41 "C 300-MHz lH NMR spectrum of 2 exhibited SCH, resonances a t 6 2.60 and 2.59 (9). Additional spectra were recorded as the probe temperature was raised in 10 "C increments. At -11 "C, the two SCH, resonances coalesced to a broad singlet a t 6 2.59. Severe broadening of the two ReCH, resonances also occurred, and these disappeared into the base line at higher temperatures. From these data, AG*262 = 14.2 kcal/mol was calculated for the process equivalencing the SCH, groups.12 The -27 "C 75-MHz 13CNMR spectrum of 2 exhibited SCH3resonances at 34.1 and 28.0 (s) ppm. Additional spectra were recorded as the probe temperature was raised. At 16 "C, the two SCH, resonances merged into the base line. At 27 "C, only one SCH, resonance was observed (31.0 ppm). From these data, AG', = 12.9 kcal/mol was calculated for the process equivalencing the SCH, groups.12 Since pyramidal inversion barriers in sulfonium salts are generally >25 kcal/mol,13 a dissociative mechanism was suspected for the above dynamic behavior. Accordingly, when CH3SCH3 (1.5 equiv) was added to 2 in CD2C12at -37 "C, SCH3 'H NMR resonances (300 MHz) were observed a t 6 2.60 (br s, 2 , 6 H), and 6 2.06 (s, CH3SCH3,9 H). At or above 12 "C, only a single resonance (6 2.34) was observed for all 15 SCH, protons. A t -27 "C, SCH, 13C NMR resonances were observed a t 17.7 (CH3SCH3),28.0, and 34.1 (2) ppm. A t 32 "C, only a single SCH, resonance (23.5 ppm) was observed. These data indicate that exchange of the CH3SCH3moiety of 2 with free CH3SCH3 is facile. As would be expected from the above data, nucleophiles readily displaced CH3SCH3from 2. Thus, reaction of 2 with PPh, (CH,CN, 25 "C, 0.5 h) gave the previously reported phosphonium salt [ (q5-C5H5)Re(NO)(PPh,)(CH2PPh3)]+PF6-(4)& in quantitative spectroscopic and 76% isolated yield. In a 'H NMR monitored experiment, pyridine (1.6 equiv) and 2 reacted (CD,CN, 25 "C, 0.2 h) to give the previously reported pyridinium salt
Organometallics, Vol. 5, No. 9, 1986 1779
I 2 CH3
I
\fi
4
? /Re\
/Re\ ON PPh3 HC \SR
I
I
ON PPhj H2C\&
fie, R = CHI & , R = C6Hs SIR = CH2CsH5
3
pFS-
5
or CH3SSCH3(51%, isolated). The spectroscopic properties of 7+PF, were similar to those of 2, except that lH and 13CNMR showed 7+PF6-to exist as a ca. 2:l:l mixture of three diastereomers. The diastereomer ratio was unaltered by numerous recrystallizations and purification attempts, suggesting eq 3 to be readily reversible. Accordingly, in 70 "C 'H NMR spectra (CDC12CDC12),7+PF, exhibited a single broad asymmetric q5-C5H5resonance.
1'
1
PF6-
In a spectroscopically monitored experiment (CDCl,, 25 "C, 30(n no. of variables abs coeff ( p ) , cm-' min transmissn av transmissn dcalcd,
goodness of fit largest shift/error in final cycle
4 1.71
0.21 x 0.12 x 0.09 Mo Kru (A = 0.71069) 23 w-26
1-20 (variable) h (0-21), k (0-23), l(0-15) 1.0 + 0.350 tan 6
48.0 97 4133 2747 333 53.3 0.685 0.778 0.038 0.052 1.71
0.15
C23
C
Figure 1. Structure and atomic numbering of the cationic portion of [($-C5H5)Re(NO)(PPh3)(CH2-)]2S+CH3 I-.(CH,CN), (7+I-. (CH3CN),. Primed and unprimed atoms are on opposite sides of the symmetry plane.
6
V I 0
11
5 _
to those of 2 and 7+PF6-and was, by all criteria, a single diastereomer. In contrast to 2 and 7+PF6-, 10 reacted only sluggishly with PPh, (65 "C, CH,CN, 0.5 h; >50% of 10 remaining) to yield the phosphonium salt 4 and an unidentified v5-CSH5-containingproduct.
Discussion Sulfonium salts that are substituted with a transition metal at an a-carbon, L,MCHRS+R'R", are often referred to as sulfur ylide ~omplexes.'~Previously, most sulfur ylide complexes have been prepared by displacement of (14) Weber, L. Angew. Chem., Int. Ed. Engl. 1983,22,516.
Figure 2. Newman-type projection down the C24-Re bond vector in 7+1-.(CH3CN),.
an existing ligand by a free sulfur ylide.'* However, related phosphorus and nitrogen complexes are often synthesized from the corresponding alkylidene complex L,M=CHR (or a precursor) and heteroatom nucleophile.*a~c~15-17 (15) Schmidbaur, H. Angew. Chem., Int. Ed. Engl. 1983, 22, 907. (16)Nakazawa, H.; Johnson, D. L.; Gladysz, J. A. Organometallics 1983,2,1846.
Metal Complexes of Sulfur-Containing Ligands Table 11. Positional Parameters and Equivalent Isotropic Thermal Parameters for Non-Hydrogen Atoms in 7+I-* (CH&N), and Their Estimated Standard Deviations atom B," A2 Y 2 X Re I S P 0 N1 N2b N3b C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 C14 C15 C16 C17 C18 C19 C20 C21 C22 C23 C24 C25 C27b C28b C2gb C30b
0.37909 (2) 0.14482 (6) 0.3785 (2) 0.3430 (1) 0.5355 (3) 0.4725 (4) 0.354 (1) 0.653 (1) 0.3571 (5) 0.4247 (6) 0.4416 (6) 0.3857 (7) 0.3183 (7) 0.3047 (7) 0.2461 (4) 0.2206 (5) 0.1482 (6) 0.1016 (5) 0.1224 (5) 0.1953 (5) 0.3873 (5) 0.3915 (6) 0.4223 (7) 0.4504 (7) 0.4479 (7) 0.4166 (6) 0.3864 (5) 0.3373 (6) 0.2783 (5) 0.2927 (6) 0.3623 (6) 0.3465 (5) 0.4744 (9) 0.2177 (9) 0.293 (1) 0.667 (1) 0.661 (1)
0.91001 (2) 0.750 0.750 0.9566 (1) 0.9067 (3) 0.9083 (3) 0.750 0.750 0.9099 (4) 0.8830 (5) 0.8486 (6) 0.8386 (6) 0.8629 (8) 0.8969 (5) 0.9764 (4) 1.0380 (5) 1.0507 (5) 1.0020 (7) 0.9368 (6) 0.9244 (5) 1.0335 (4) 1.0529 (5) 1.1093 (5) 1.1493 (5) 1.1315 (5) 1.0723 (5) 0.9492 (5) 0.9877 (5) 0.9470 (7) 0.8867 (5) 0.8850 (5) 0.8189 (4) 0.750 0.750 0.750 0.750 0.750
0.44441 (2) 0.45288 (7j 0.4471 (2) 0.2978 (2) 0.3958 (6) 0.4135 (6) 0.784 (1) 0.511 (2) 0.1909 (6) 0.1740 (7) 0.0936 (8) 0.0272 (8) 0.0411 (7) 0.1219 (8) 0.3007 (6) 0.3075 (6) 0.3239 (7) 0.3343 (8) 0.327 (1) 0.3096 (8) 0.2638 (7) 0.1700 (8) 0.1455 (9) 0.215 (1) 0.308 (1) 0.3347 (9) 0.5935 (7) 0.5469 (7) 0.5269 (7) 0.5618 (7) 0.6008 (7) 0.3801 (6) 0.416 (2) 0.748 (2) 0.770 (1) 0.329 (2) 0.433 (2)
3.028 (71 4.97 (2) 3.92 (7) 3.35 (5) 5.7 (2) 3.3 (2) 10.4 (6) 25 (2) 3.6 (2) 5.0 (2) 5.6 (3) 7.1 (3) 7.2 (4) 5.4 (3) 3.5 (2) 4.3 (2) 5.3 (2) 6.6 (3) 6.2 (3) 5.0 (3) 4.2 (2) 5.5 (3) 7.1 (3) 7.6 (3) 7.2 (3) 5.8 (3) 4.7 (2) 5.1 (2) 6.5 (3) 5.6 (3) 5.2 (3) 3.4 (2) 9.5 (6) 10.1 (7) 7.5 (5) 11.6 (8) 15 (1)
"Defined as (4/3)[a2Bn + b2Bzz+ c2B33+ ab(cos 7 ) B I 2+ ac(cos P)BI3+ bc(cos a)BZ3].bThe solvate atoms are C27-C28-N2 and C29-C30-N3; other atoms are numbered as in Figure 1.
Table 111. Bond Distances (A) in 7'1-0 (CH3CN),with Estimated Standard Deviations in Parentheses Re-Nl Re-P Re-C19 Re-C20 Re421 Re422 Re-C23 Re-Cp" Re-C24 SG24 S-C25 N1-0 P-c 1 P47 P-C13 Cl-C2 Cl-C6 C2-C3 c3-c4 c4-c5 C5-C6
1.767 (6) 2.357 (2) 2.237 (8) 2.287 (8) 2.309 (8) 2.330 (8) 2.263 (8) 1.955 2.178 (6) 1.807 (7) 1.813 (15) 1.182 (7) 1.796 (7) 1.826 (7) 1.855 (8) 1.379 (11) 1.388 (11) 1.366 (12) 1.397 (14) 1.349 (14) 1.352 (13)
C7-C8 C7-Cl2 C8-C9 c9-c10 ClO-Cll Cll-C12 C13-Cl4 C13-Cl8 C14-Cl5 C15-Cl6 C16-Cl7 C17-Cl8 C19-C20 C19-C23 C20-c21 C21-C22 C22-C23 N2-C28b C27-C28b N3-C30b C29-C30b
1.366 (10) 1.431 (10) 1.374 (11) 1.333 (14) 1.410 (15) 1.386 (11) 1.372 (11) 1.384 (12) 1.345 (12) 1.38 (2) 1.346 (14) 1.406 (12) 1.369 (12) 1.409 (13) 1.400 (13) 1.368 (14) 1.388 (13) 1.13 (2) 1.43 (2) 1.08 (3) 1.46 (3)
"Distance from Re to the $'-C5H5 plane. bSolvate atoms; other atoms are numbers as in Figure 1.
Equation 1 is, to our knowledge, the only sulfur ylid? complex synthesis from an isolable or detectable alkylidene complex. Sulfur ylide complexes have also been prepared (17) Fischer, H.; Weber, L. Chern. Ber. 1984, 117, 3340.
Organometallics, Vol. 5, No. 9, 1986 1781 Table IV. Bond Angles (deg) in 7+I-*(CH3CN),with Estimated Standard Deviations in Parentheses P-Re-N1 P-Re-C19 P-Re-C20 P-Re-C21 P-Re-C22 P-Re-C23 P-Re-C24 N1-Re-C 19 Nl-Re-C20 Nl-Re-C21 Nl-Re-C22 Nl-Re-C23 Nl-Re-C24 C19-Re-C20 C19-Re-C2 1 C19-Re-C22 C19-Re-C23 C19-Re-C24 C20-Re-C21 C20-Re-C22 C20-Re-C23 C20-Re-C24 C21-Re-C22 C21-Re-C23 C21-Re-C24 C22-Re-C23 C22-Re-C 24 C23-Re-C24 Re-N1-0 Cl-P-C7 c1-P-c13 c7-P-c 13 C24-S-C24'
94.0 (2) 132.4 (3) 99.1 (2) 94.1 (3) 120.2 (3) 153.1 (3) 85.5 (2) 100.1 (3) 119.5 (3) 154.8 (3) 145.8 (4) 111.3 (3) 98.5 (3) 35.2 (3) 57.6 (3) 57.5 (3) 36.5 (3) 135.7 (3) 35.5 (4) 58.6 (3) 60.9 (3) 141.1 (3) 34.3 (4) 59.1 (3) 105.9 (4) 35.1 (3) 85.6 (3) 99.2 (3) 177.9 (6) 106.3 (4) 100.9 (4) 103.8 (3) 104.7 (5)
c24-s-c25P-Cl-C2 P-C1-C6 C2-Cl-C6 Cl-C2-C3 c2-c3-c4 c3-c4-c5 C4-C5-C6 Cl-C6-C5 P-C7-C8 P-c7-c 12 C8-C7-C12 C7-C8-C 9 C8-C9-C10 c9-c10-c 11 C1O-Cl1-C12 C7-Cl2-Cll P-Cl3-Cl4 P-Cl3-Cl8 C14-C 13-C 18 c13-c 14-c15 C14-Cl5-Cl6 C15-CI6-Cl7 C16-Cl7-Cl8 C13-Cl8-Cl7 c20-c 19-c23 c19-c2o-c21 c2o-c21-c22 c21-c22-c23 c19-c23-c22 Re-C24-S N2-C28-C27" N3-C30-C29"
101.0 (5) 119.4 (6) 125.4 (6) 115.2 (7) 123.8 (8) 117.1 (9) 121.4 (9) 119.0 (9) 123.4 (9) 123.0 (6) 117.7 (6) 118.6 (7) 121.4 (8) 119.6 (9) 123.2 (8) 116.9 (8) 120.2 (8) 121.4 (7) 119.4 (6) 119.2 (8) 121 (1) 120 (1) 119.8 (8) 121 (1)
118.5 (9) 112.3 (8) 104.5 (9) 109.4 (8) 109.9 (8) 103.7 (8) 112.7 (3) 177 (2) 177 (2)
Solvate atoms; other atoms are numbered as in Figure 1.
by direct or assisted (Ag+,T1+)displacement of halides in halomethyl complexes L,MCH2X by ~ u l f i d e s ' ~and J ~ by alkylation of a-(alky1thio)alkyl complexes L,MCHRSR'.1g-21 The addition of phosphine and amine nucleophiles to alkylidene complexes is an equilibrium process. Several studies have shown that the principal factors influencing K,, are nucleophile basicity, alkylidene complex Lewis acidity, and steric effects.22 The reaction of methylidene complex 1 and CH3SCH3to give sulfonium salt 2 is clearly reversible, as indicated by the NMR properties of 2 and further suggested by the facile nucleophilic displacement of CH3SCH3from 2 (eq 2). Several Kq trends are evident in our chemistry. First, organic sulfides bulkier than CH3SCH3 fail to give stable adducts with 1. Second, bulkier and less Lewis acidic alkylidene complexes ac[ (q5-C,H5)Re(NO)(PPh3)(=CHR)]+PF6fail to react with CH3SCH3. However, one K,, trend is to our knowledge without precedent. Equation 5 shows that the basicity of bulky organometallic sulfide 6a toward 1 is greater than that of CH3SCH3! Note also that pyridine (1.6 equiv) completely (18) (a) Werner, H.; Paul, W.; Feser, R.; Zalk, R.; Thometzek, P. Chem. Ber. 1985, 118, 261. (b) Bodnar, T. W.; Cutler, A. R. Organometallics 1985,4, 1558. (c) Barefield, E. K.; McCarten, P.; Hillhouse, M. C. Ibid.
1985, 4, 1682. (19) (a) Brandt, S.; Helquist, P. J. Am. Chern. SOC. 1979, 101, 6473. (b) Kremer, K. A. M.; Helquist, P.; Kerber, R. C. Ibid. 1981, 103, 1862. (c) O'Connor, E. J.; Helquist, P. Ibid. 1982, 104, 1869. (d) Kremer, K. A. M. Ph.D. Thesis, SUNY Stony Brook, 1982. (e) O'Connor, E. J. Jr. Ph.D. Thesis, SUNY Stony Brook, 1984. (20) Collins, T. J.; Roper, W. R. J. Organornet. Chem. 1978, 159, 73. (21) Davidson, J. G.; Barefield, E. K.; Van Derveer, D. G. Organometallics 1985,4, 1178. (22) (a) Fischer, H.; Fischer, E. 0.; Kreiter, C. G.; Werner, H. Chem. Ber. 1974,107,2459. (b) Fischer, H. J.Organornet. Chem. 1979,170,309. (c) Choi, H. S.; Sweigart, D. A. Ibid. 1982, 228, 249.
1782 Organometallics, Vol. 5, No. 9, 1986
McCormick et al.
displaces CH3SCH3 from 2, but not 6a from 7+PF;. Therefore, Keqfor eq 3 must be greater than that for eq 1. This suggests that some electronic effect confers enhanced basicity upon the sulfide sulfur atom in 6a. It is well-known that C, of transition-metal allyl complexes, L,MCH2CH=CH2, is rendered exceptionally nucleophilic via hyperconjugation of the olefin T cloud with the M-C CT bond.23 We suggest that a similar interaction provides enhanced basicity to heteroatoms with lone electron pairs that are 6 to transition Although K , for eq 3 is greater than that for eq 1, several observations suggest that eq 3 is readily reversible. First, no deviation from the ca. 2:l:l mixture of 7+PF6diastereomers is observed under a variety of recrystallization conditions. Second, the q5-C5H5'H NMR resonances of these diastereomers begin to coalesce at elevated temperatures. Third, PPh3 converts 7+PF6-to a 1:l mixture of 6a and 4 (eq 4). Finally, we have previously reported that methoxymethyl complex (q5-C5H5)Re(NO)(PPh3)(CH20CH3)readily transfers an a-hydride to methylidene complex 1 a t -78 'C to give methyl complex 8 and methoxymethylidene complex [ (q5-C5H5)Re(NO)(PPh3)(=CHOCH3)]+PF6-.Ba The formation of 8 and (methy1thio)methylidene complex 9 from the thermal decomposition of 7+PFc (eq 4) suggests initial dissociation to (methy1thio)methyl complex 6a and methylidene complex 1, followed by an analogous hydride transfer. Surprisingly, thiocarbene complexes of the formula L,M= CHSR, such as 9, are relatively u n c ~ m r n o n . ~ ~ ~ ~ ~ Although we have not yet been able to cleanly synthesize thioether complex [(q5-C5H,)Re(NO)(PPh3)(CH,-)],S (11, eq 6), we suggest that the sulfide sulfur in this compound would be even more basic than that in 6a. As evidence, we note the facile formation of trinuclear sulfonium salt 10 in eq 6 . Furthermore, we could not effect any welldefined carbon-sulfur bond cleavage reactions of 10 under conditions where 2 or 7+?F6- would have reacted rapidly. This suggests that Kes for the last step of eq 6 (11 + 1 10) is larger than that for eq 3. Trinuclear complex 10 is, to our knowledge, the only known example of a a,a',a"tris-metalated sulfonium salt. The above data are particularly relevant to recent studies of Helquist and co-w~rkers.'~ They have reported syntheses of the iron sulfonium salts [ (q5-C5H5)Fe(CO),CH2S(CH3),]+BF4- ( 12+BF4-) and [(q5-C5H5)Fe(CO)zCH&4(CH3)2]+FS03(12+FSO
